There was an Asian chick with a purple streak in her hair that didn't have any of the same powers as Psylocke, and was never referred to as Psylocke, Betsy, Elizabeth, or Braddock.

Basically, her involvement in X-Men 3 was no more than Beast's involvement in X-Men 2, and using her in a later movie in a proper role is no more a contradiction than Beast in X-Men 3 and X-Men: First Class were to X-Men 2.